- Implement CSS styles for missing models browser interface (.ml-missing-browser and related classes)
- Add JavaScript methods for handling missing models:
* getMissingModelKey, getMissingFilename, getBestLocalMatch
* getMissingModelSummaryStats, getMissingSourceStatus
* renderMissingSourcesSummary, hasRenderableSearchState
- Replace missing models rendering logic with new implementation
- Support for exact/partial match statistics and source status indicators